Currently, ships with a total tonnage of 20 tons and more are requested to be equipped with a global maritime distress and safety system (GMDSS) as a radio communication system throughout the world (Japanese Laid-open Patent Publication No. 2001-283145 and Japanese Laid-open Patent Publication No. 2008-009846, “Maritime Radio Communication System”, [Online], [Searched on Mar. 5, 2014], Internet <http:www.soumu.go.jp/soutsu/tokai/musen/kaijou/>, “GMDSS MASTER PLAN”, [Online], [Searched on Mar. 4, 2014], Internet <http://www.imo.org/blast/blastDataHelper.asp?data_id=30623&filename=13.pdf>). However, because the GMDSS is expensive, fishing boats with a total tonnage less than 20 tons are exempted from equipment of GMDSS by practicing “presumptive GMDSS” of orally reporting position information three times a day to the fishery radio communication association responsible for the fishing boats by using a fishery radio.
However, in the presumptive GMDSS, receiving reports from a lot of fishing boats on a 24-hour basis, work of the fishery radio communication association is hard. Moreover, as the fishery radio communication is a voice communication using, for example, a high frequency band such as a single side band (SSB), the reception varies depending on the condition of ionosphere, and communication can be difficult. Therefore, the fishery radio communication association loses contact with a fishing boat, and it is difficult to be aware of the state of the fishing boat, and management of ships is to be difficult. Not limited to the presumptive GMDSS, communicating between land and ships can be similarly difficult, and management of ships is to be difficult.